In order to be useful in fuel cells such as Solid Oxide Fuel Cells (SOFCs), anodes (fuel electrodes) must possess a high performance in terms of high electrochemical activity and high redox stability. Current state of the art Ni—YSZ anodes provide a reasonable electrochemical activity at high operating temperatures often above 80° C. but are normally not redox stable. Volume changes in Ni—YSZ anodes due to reduction and oxidation of Ni results in inexpedient mechanical stresses in the anode material which impair the performance of the fuel cell.
In “Synthesis of Nb-doped SrTiO3 by a modified glycine-nitrate process”, Journal of the European Ceramic Society, 2007 by Blennow et al. a method of preparing submicronic particles of Nb-doped strontium titanate for use in SOFC anodes is disclosed.
US-A1-2005/0250000 Marina et al. discloses an anode having two separate phases, one of doped strontium titanate and one of doped ceria; the ceria contains Nb, V, Sb or Ta. The strontium titanate phase is the more electronically conductive but has poor electrocatalytic activity. Ceria is on the other hand active in hydrocarbon oxidation but has poor electronic conductivity.
In “Ni/YSZ and Ni—CeO2/YSZ anodes prepared by impregnation of a solid oxide fuel cell”, Journal of Power Sources, Qiao et al. disclose the preparation of Ni—CeO2/YSZ anodes by tape casting and vacuum impregnation. The addition of CeO2 is said to enhance cell performance.
U.S. Pat. No. 5,350,641 Mogensen et al. discloses the use of CeO2-based ceramics as the anode in a fuel cell.
U.S. Pat. No. 6,752,979 Talbot et al. discloses the preparation of nano-sized ceria particles with templating surfactants. The removal of the surfactant and attendant formation of nano-sized particles having grain sizes of 2-10 nm is effected by calcination at e.g. 300° C.
In “Mesoporous thin films of high-surface-area crystalline cerium dioxide”, Microporous and Mesoporous Materials 54 (2002), 97-103, Lunderg et al. disclose the formation of nano-sized ceria particles by the removal of templating surfactant during calcination at about 400° C.
WO-A-2006/116153 discloses a method of forming a continuous network of fine particles on the pore walls of a porous structure in a single step by removing the solvent of a solution containing a metal salt, surfactant and solvent prior to infiltration. The removal of the solvent is conducted by heating.
WO-A-2005/122300 describes metal supported anode structures manufactured from powder suspensions containing FeCr alloy, a layer for anode impregnation comprising ScYSZ and FeCr alloy, an electrolyte layer. The thus obtained half-cells are sintered and a solution of Ni, Ce, Gd nitrates is impregnated into the anode layer by vacuum infiltration thus resulting in an anode containing 40 vol % Ni. A cathode layer is subsequently deposited on the electrolyte surface. This application is, however, silent about the provision of nano-sized ceria particles within an electronically conductive phase of doped strontium titanate acting as anode support.
US-A1-2004/0018409 is concerned with the fabrication of a solid oxide fuel cell in which the anode, cathode and electrolyte are produced by thermal spraying. The anode may contain yttrium-doped strontium titanate. This application is, however, also completely silent about the provision through impregnation of nano-sized ceria particles within an electronically conductive phase of doped strontium titanate.